I was the coticule under-acheiver for a dang long time. I get fine edges now with them, but it took more blades to learn than others.

I absolutely agree that synthetics come first - then whatever your heart desires and wallet tolerates.

As to natural combo - 2 of the 3 I have are naturals. I found it easier to get the sharpness on the BBW, using a technique I learned elsewhere. Sharpness was close to that of a Naniwa 12k, using spine-leading strokes on a very light slurry. The resulting edge was more crispy/harsh than I prefer, but then you can use the Yellow side to bring back the smoothness.